In a radio air-interface of cellular networks, the more the channel status information (CSI) is available at the transmission side of access point (AP), the better downlink (DL) performance the system can achieve. Though uplink (UL) and downlink (DL) are facing different interferences, the channel reciprocity of Time Division Duplex (TDD) systems enables effective and accurate uplink/downlink channel information sharing between the access point (AP) and the user equipment (UE). Thus, by taking this advantage, TDD system can employ the shared comprehensive channel information to further improve the downlink performance.
However, owing to contradiction between a large number of UEs and the limited feedback capacity or sounding capacity of the existing system, only partial or coarse CSI of the downlink is available at access point for each UE.